1. Field of the Invention
The present invention relates to a cool air circulation type axial flow fan for a refrigerator which is capable of blowing cool air to a freezing chamber and a chilling chamber, and more particularly to a cool air circulation type axial flow fan for a refrigerator in which several important design factors of the fan can be optimally determined to reduce flow noise over a relatively wide frequency band.
2. Description of the Related Art
Generally, a refrigerator stores foodstuffs in a fresh state for a long time using cool air obtained by a refrigerating cycle. The cool air is used to cool down the foodstuffs or prevent decomposition of the foodstuffs. A cool air circulating fan is disposed in a flow channel through which the cool air is circulated for blowing the cool air to a chilling chamber or a freezing chamber.
FIG. 1 is a side view, in longitudinal section, of a general refrigerator. FIG. 2 is a front view of a conventional cool air circulation type axial flow fan, and FIG. 3 is a side view of the conventional cool air circulation type axial flow fan.
As shown in FIG. 1, the refrigerator basically comprises a outer case 1 having an open front part, an inner case 2 disposed in the outer case 1 and spaced apart from the outer case 2, a chilling chamber A mounted at the upper part in the inner case 2, a freezing chamber B mounted at the lower part in the inner case 2, a machinery chamber C provided below the freezing chamber B, a door 3 pivotably attached at the upper front part to the outer case 1, and another door 4 pivotably attached at the lower front part to the outer case 1.
Between the outer case 1 and the inner case 2 is defined a flow channel, through which the cool air is supplied to the chilling chamber A or the freezing chamber B. In the flow channel at the freezing chamber B is mounted an evaporator 5 for producing the cool air by heat exchange with atmospheric air. In the flow channel above the evaporator 5 is mounted a blower 10 for upwardly blowing the cool air having passed through the evaporator 5.
In the machinery chamber C are mounted a compressor 6 connected to the evaporator 5 via a refrigerant pipe, a condenser (not shown), and an expander (not shown), which constitute together a refrigerating cycle to generate the cool air. The resulting cool air is supplied to the chilling chamber A or the freezing chamber B. Consequently, the chilling chamber A or the freezing chamber B are maintained at low temperatures, respectively.
The blower 10 includes an axial flow fan 12 attached to a rotating shaft of a motor for blowing the cool air. As shown in FIG. 2, the axial flow fan 12 comprises a hub 12a attached to the motor via the rotating shaft of the motor, and four spaced blades 12b mounted on the outer circumference of the hub 12a. 
Each of the blades 12b has a leading edge LE facing the direction of rotation, a trailing edge TE opposite to the leading edge, a blade tip BT connected between the outer ends of the leading and trailing edges LE and TE, and a blade hub BH connected to the hub 12a. 
Each of the blades 12b also has a front surface P to which a pressure created by the introduced cool air is applied (hereinafter referred to as a positive pressure surface P), and a rear surface D opposite to the positive pressure surface P (hereinafter referred to as a negative pressure surface D).
Each of the blades 12b is formed in such a manner that a sweep angel α of each of the blades 12b is relatively small, for example, approximately 25 degrees.
The sweep angle α indicates the degree in which each of the blades 12a is inclined from the radius of the fan toward the direction of rotation. Specifically, the sweep angle α is an angle defined between a line connecting the center of the blade hub BH to the center of the blade tip BT and an extension of another line connecting the center of the hub 12a to center of the blade hub BH.
When the conventional cool air circulation type axial flow fan 12 with the afore-stated construction is operated by means of the motor, the sweep angle α is relatively small. Consequently, a sufficient strong cool air flow suitable for a large pressure loss occurring across a complex flow channel in a large-sized refrigerator is not created. Furthermore, the cool air flow advances in the axial direction of the fan with the result that noise is increased.